A. Field of the Invention
The present invention relates to a nuclear medicine imaging apparatus and a method for displaying image data thereof, and more particularly, to a positron emission computer tomography (PET) apparatus and a method for displaying image data thereof that can automatically restart data collection of image data by detecting impermissible body movement of an object during the image data collection.
B. Background of the Invention
Recent developments of computer technologies have rapidly progressed medical imaging apparatus, such as an X-ray diagnosis apparatus, a magnetic resonance imaging (MRI) apparatus, an X-ray computer tomography (CT) apparatus and a nuclear medicine imaging apparatus. A nuclear medicine imaging apparatus can display distribution image data of a radioactive isotope in an object by detecting gamma-rays emitted from the object injected with the radioactive isotope.
X-ray diagnosis apparatus and X-ray CT apparatus are usually aimed for use in a so-called morphology diagnosis involving displaying images of profile of internal organs or tumors in an object. On the contrary, a nuclear medicine imaging apparatus is used for a faculty diagnosis of an object through imaging a dosage distribution by measuring gamma-rays emitted from a radioactive isotope that has been selectively introduced into organs of a living body or is emitted from a marked medicine by a radioactive isotope.
As a nuclear medicine imaging apparatus for a clinical diagnosis, a gamma camera, a single photon emission CT (SPECT) apparatus or a positron emission computer tomography (PET) apparatus are usually used.
A gamma camera includes a plane detector facing an object in order to display a distribution of radioactive isotope projected on the plane detector as a two-dimensional image by measuring gamma-rays emitted from an object. The gamma camera specifies incident directions of a gamma ray into the plane detector through a collimator that is provided in front of the plane detector.
A SPECT apparatus also provides a similar plane detector in a gamma camera, in which a plane detector is moved around an object or a plurality of plane detectors are moved around an object. In the SPECT apparatus, image data are generated by performing a reconstruction process similar to that used in an X-ray CT apparatus based on detected gamma-ray data of single photon emitted in a plurality of directions from an object.
A PET apparatus detects a pair of gamma-rays emitted from an object through a ring-like detector that is provided around an object in order to generate image data by performing a reconstruction process of the gamma-rays detected through the detector. Usually, an object is administered (injected) with a medicine marked with a nuclide so as emit positrons before the object is placed into the PET apparatus. During data collection in the PET apparatus, a pair of gamma-rays is emitted in almost opposite directions when a positron couples with an electron. Usually, each of a pair of gamma-rays is 511 keV (kilo-electron volts). The pair of gamma-rays emitted from an object is detected through the ring-like detector.
The SPECT apparatus includes two-dimensional detectors and the PET apparatus includes a plurality of ring-like detectors. Each of these detectors is comprised of a plurality of scintillators for converting each gamma-ray to light and a plurality of photomultipliers (PMTs) for amplifying the light and for converting the light into electrical signals. For instance, Japanese Patent Application Publication 2002-90458 suggests performing an image reconstruction process by using the count value of gamma-rays detected by a detector module during a prescribed time as projection data.
To generate image data through a nuclear medicine imaging apparatus, a doctor or an examination engineer (hereinafter referred to as an operator) needs to collect projection data from a wide diagnosis area over an object by and to perform an image reconstruction process of the collected projection data. For the projection data used in the reconstruction process, count values of gamma-rays that are detected through the detector during a prescribed data collecting period (hereinafter simply referred to as a data collecting period) are used. Usually, in PET apparatus, a data collecting time for a predetermined diagnosis portion □Z along a body axis of an object is about two minutes. Accordingly, to collect project ion data in a wide scope of diagnosis, the detector is moved step by step over a predetermined scope by the predetermined diagnosis portion □Z. For instance, if it is required s to move the detector by 10 steps for collecting projection data for a required diagnosis scope, it takes more than twenty minutes.
Consequently, the patient may move his body during such a long data collecting time for a wide diagnosis area of an object. When a patient moves his body during such a data collecting time (hereinafter, simply, “a body movement ”has occurred), a problem in the image quality of image data being generated based on such projection data conventionally occurred. Thus, image quality deteriorates due to body movement. When an operator observes such image deterioration due to body movement after finishing reproduction of image data, the collection of projection data needs to be restarted from an initial step in order to generate image data and to execute a reconstruction process based on the recollected projection data.
Consequently, data collection takes longer due to the need for restarting image data generation. This seriously reduces examination efficiency and it also imposes a great deal of physical burden both on the patient and operator. Moreover, if a radioactive isotope has a rather short radioactive half-life, if the radioactive isotope needs to be administered again into a patient, a total amount of radioactive contamination for a patient seriously increases due to restart of projection data. These are serious problems in a conventional PET apparatus.
The present invention is capable of solving the above-mentioned problems and defects of the conventional nuclear image processing apparatus. The present invention provides a PET imaging apparatus and an image generation method thereof that can restart a collection of projection data at an early stage when a non-permissible body movement occurs. Thus, a PET imaging apparatus consistent with the present invention detects such body movement by monitoring a variation of count values of gamma-rays emitted from a patient who has been administered a radioactive isotope.